1. Field of the Invention
The present invention relates to water-softening compositions having improved biodegradability.
2. Discussion of the Background
The function of a water softener is to eliminate the calcium and magnesium ions from the water used in a washing process by complexation, dispersion and sequestration and thereby augment the detergent action of the surfactants used in the washing process. The softeners reduce the formation of deposits in the washing machine, for example on the heating elements.
According to J. Falbe, Surfactants in Consumer Products, pp. 292-293 (1987), water softeners conventionally predominantly comprise phosphates or mixtures of phosphates, zeolites and polycarboxylates. Although both types of softeners have a good ability to bind alkaline earth metal ions and an excellent dispersing and dirt-carrying ability, they have ecological disadvantages. Specifically, pollution of the wastewater with phosphates leads to over fertilization of natural waters and to the problems associated with eutrophication.
Combinations of zeolites and polycarboxylates are frequently used as substitutes for phosphates. Thus, DE-A-39 31 871 describes phosphate-free water-softening agents which predominantly comprise zeolite, sheet silicate and the sodium salt of a polycarboxylic acid, preferably an acrylic acid/maleic acid copolymer. A disadvantage of the polycarboxylates used today is that the polymers have only a low biodegradability and are therefore mineralized only to a small extent in a water treatment plant.
Thus, there remains a need for water-softening compositions which are free of the above-described drawbacks.